Photopolymerizable composition, photopolymerizable ink jet ink, ink cartridge, and coated matter

ABSTRACT

A photopolymerizable composition includes diethyleneglycol dimethacrylate and methacrylic acid ester having a phosphoric group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Applications Nos. 2013-091979 and 2014-035223, filed on Apr. 25, 2013 and Feb. 26, 2014, respectively in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a photopolymerizable composition, and a photopolymerizable inkjet ink, an ink cartridge containing the ink and a coated matter coated therewith.

2. Description of the Related Art

PCT Japanese published national phase application No. 2004-526820 discloses a photopolymerizable composition and a photopolymerizable inkjet ink using (meth)acrylic acid ester.

However, many of monomers used in conventional photopolymerizable inkjet inks have toxicities. Particularly, inexpensive and easily-obtainable (meth)acrylic acid esters occasionally cause allergies when contacting skins.

The present inventors have found some (meth)acrylic acid esters and (meth)acryl amides having no problem of skin sensitization. As disclosed in Japanese published unexamined application No. JP-2012-140593-A, they noticed that methacrylate is less toxic than acrylate and suggested an inkjet ink mainly using methacrylate.

The inkjet ink is required to have low viscosity even when including various materials such as a pigment and an additive so as not to prevent the ink from ejecting. Water can be included therein to lower the viscosity and the photopolymerizable inkjet ink including water is known. However, since penetration drying cannot be expected from non-permeable substrates as mentioned later, a process of vaporizing water is needed for higher printing speed and efficiency, resulting in enlargement of the apparatus.

When the photopolymerizable composition is used for brush coating, an organic solvent can be used. Since the organic solvent is volatilized and discharged in the atmosphere, the organic solvent is preferably used in a minimum amount in consideration of influence on the environment. On the other hand, when used as an inkjet ink, the organic solvent having high volatility occasionally increases viscosity of the ink, resulting in poor rejection thereof. The organic solvent needs adjustment in volatility for the ink to stably eject.

SUMMARY

Accordingly, one object of the present invention is to provide a photopolymerizable composition having no problem of skin sensitization and improved adherence to metal surfaces.

Another object of the present invention is to provide a photopolymerizable inkjet ink using the photopolymerizable composition.

A further object of the present invention is to provide an ink cartridge containing the inkjet ink.

Another object of the present invention is to provide a coated matter using the photopolymerizable composition.

These objects and other objects of the present invention, either individually or collectively, have been satisfied by the discovery of a photopolymerizable composition including diethyleneglycol dimethacrylate and methacrylic acid ester having a phosphoric group.

These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the detailed description when considered in connection with the accompanying drawings in which like reference characters designate like corresponding parts throughout and wherein:

FIG. 1 is a schematic view illustrating an example of an ink bag of the ink cartridge of the present invention; and

FIG. 2 is a schematic view illustrating an example of the ink cartridge of the present invention housing the ink bag.

DETAILED DESCRIPTION

In some cases, on a chassis or a molded product, a metallic layer such as aluminum and stainless is formed to impart metallic gloss thereto for the purpose of improving design. However, conventional photopolymerizable compositions are difficult to adhere to the surface of a metal to prevent the surface from eroding or protect the surface.

Because of these reasons, a need exists for a photopolymerizable composition and a photopolymerizable inkjet ink having no problem of skin sensitization and improved adherence to metal surfaces.

The present invention provides a photopolymerizable composition (an ink) having no problem of skin sensitization and improved adherence to metal surfaces.

More particularly, the present invention relates to a photopolymerizable composition including diethyleneglycol dimethacrylate and methacrylic acid ester having a phosphoric group.

Further, the present inventors found a photopolymerizable composition including caprolactone-modified dipentaerythritol hexaacrylate and/or ethyleneoxide-modified trimethylolpropane trimethacrylate as well improves in strength of a coating film formed therewith.

The ethyleneoxide-modified trimethylol propane trimethacrylate has a formula [CH₃CH₂C—{(CH₂(O—CH₂CH₂)_(x)—OCOC(CH₃)═CH₂}₃]. X represents a length of ethyleneoxide part. The larger the X, the larger the molecular weight and the higher the viscosity. The higher the viscosity, the more difficult to use as an inkjet ink material. However, monomers of a4 to a8 are expected to improve processing suitability. It is preferable not to use trimethylol propane trimethacrylate (x=0) because of having a symbol mark “N” representing environmental dangerous hazardousness and a risk phrase “R51/53” representing acute aquatic toxicity and long-term adverse affect in EU. Directive 67/548/EEC in consideration of influence on the environment.

X of the ethyleneoxide-modified trimethylol propane trimethacrylate used in Examples is 1. The ethyleneoxide-modified trimethylol propane trimethacrylate does not have a problem of viscosity as a material included in an inkjet ink. The photopolymerizable composition including this forms a coating film having sufficient strength. Further, the ethyleneoxide-modified trimethylol propane trimethacrylate has no problem of skin sensitization, environmental dangerous hazardousness, acute aquatic toxicity and long-term adverse affect.

The photopolymerizable composition negative for skin sensitization refers to a compound satisfying at least the following (1) or (2):

(1) a compound having a Stimulation Index (SI value) of less than 3, where the Stimulation Index indicates the level of sensitization as measured by a skin sensitization test based on the LLNA (Local Lymph Node Assay); and (2) a compound evaluated as “negative for skin sensitization” or “no skin sensitization” in its MSDS (Material Safety Data Sheet).

Regarding the above (1), the compound having the SI value of less than 3 is considered as negative for skin sensitization as described in literatures, for example, “Functional Material” (Kino Zairyou) 2005, September, Vol. 25, No. 9, p. 55. The lower SI value means the lower level of skin sensitization. Thus, in the present invention, a monomer having the lower SI value is preferably used. The SI value of the monomer used is preferably less than 3, more preferably 2 or lower, and even more preferably 1.6 or lower.

However, those affirmatively applied to human bodies as medical applications can be assumed to have no particular problem.

Diethyleneglycol dimethacrylate is suitably used as a material of the photopolymerizable composition usable as an inkjet ink because of having no problem of skin sensitization and low viscosity. However, the diethyleneglycol dimethacrylate does not have sufficient interaction with metal surfaces and the photopolymerizable composition is difficult to have adherence thereto. However, including the methacrylic acid ester having a phosphoric group, the photopolymerizable composition has adherence to metal surfaces such as aluminum and stainless. The photopolymerizable composition including the methacrylic acid ester having a phosphoric group, having a formula (CH₂═C(CH₃)COOCH₂CH₂O)₂—P(═O)OH has sufficient low viscosity and produces a coating film having sufficient strength.

The photopolymerizable composition preferably includes the diethyleneglycol dimethacrylate in an amount of from 45 to 80 parts by weight per 100 parts by weight of monomer components.

The methacrylic acid ester having a phosphoric group generates a strong interaction with a polarity of the phosphoric group and has a viscosity higher than that of typical methacrylic acid ester. The photopolymerizable composition preferably includes the methacrylic acid ester having a phosphoric group in an amount of from 5 to 30 parts by weight per 100 parts by weight of monomer components because of having suitable viscosity when used as an inkjet ink. The skin sensitization of the methacrylic acid ester having a phosphoric group is not evaluated, but as “Dental Material. Machine 5(1)144-154(1986)” shows, it is considered as a dental material and has no particular problem against human bodies.

Further, the photopolymerizable composition of the present invention preferably includes caprolactone-modified dipentaerythritol hexaacrylate and ethyleneoxide-modified trimethylolpropane trimethacrylate as polymerizable monomers. The photopolymerizable composition preferably includes the caprolactone-modified dipentaerythritol hexaacrylate in an amount of form 3 to 15 parts by weight, and more preferably from 5 to 10 parts by weight; the ethyleneoxide-modified trimethylolpropane trimethacrylate in an amount of form 15 to 60 parts by weight, and more preferably from 20 to 50 parts by weight per 100 parts by weight of monomer components, respectively.

When the photopolymerizable composition is used as an inkjet ink, the ink preferably has properties meeting with required specifications of an inkjet ejection head used. Various ejection heads are marketed from many manufacturers, and some of them have large ejection power to eject an ink having high viscosity and wide thermostat. The ink preferably has a viscosity of from 2 to 150 mPa·s, and more preferably from 5 to 18 mPa·s at 25° C. However, the thermostat of the ejection head can be used. When the viscosity is too high at 25° C., the head may be heated when necessary to make the ink have lower viscosity. When heated at from 45 to 60° C., the ink preferably has a viscosity of from 5 to 18 mPa·s thereat.

The following (meth)acrylates and (meth)acryl amides can be used together as long as a resulting ink does not have a problem, even though they have a problem of skin sensitization in some degrees when used alone, or skin sensitization thereof is not confirmed.

Specific examples thereof include, but are not limited to, ethylene glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, γ-butyrolactone acrylate, isobornyl(meth)acrylate, formulated trimethylol propane mono(meth)acrylate, polytetramethylene glycol di(meth)acrylate, trimethylol propane (meth)acrylic acid benzoate, diethyleneglycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate [CH₂═CH—CO(OC₂H₄)_(n)—OCOCH═CH₂(n≈9)], [CH₂═CH—CO(OC₂H₄)_(n)—OCOCH═CH₂ (n≈14)], [CH₂═CH—CO(OC₂H₄)_(n)—OCOCH═CH₂(n≈23)], dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol dimethacrylate [CH₂═C(CH₃)—CO—(OC₃H₆)_(n)—OCOC(CH₃)═CH₂(n≈7)], 1,3-butanediol diacrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, propylene oxide-modified bisphenol A di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, (meth)acryloyl morpholine, 2-hydroxypropyl (meth)acryl amide, propylene oxide-modified tetramethylol methane tetra(meth)acrylate, dipentaerythritol hydroxypenta(meth)acrylate, caprolactone-modified dipentaerythritol hydroxypenta(meth)acrylate, ditrimethylol propane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylol propane acrylate, ethylene oxide-modified trimethylol propane triacrylate, propylene oxide-modified trimethylol propane tri(meth)acrylate, caprolactone-modified trimethylol propane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, propylene oxide-modified neopentyl glycol di(meth)acrylate, propylene oxide-modified glyceryl tri(meth)acrylate, polyester di(meth)acrylate, polyester tri(meth)acrylate, polyester tetra(meth)acrylate, polyester penta(meth)acrylate, polyester poly(meth)acrylate, N-vinyl caprolactam, N-vinyl pyrrolidone, N-vinyl formamide, polyurethane di(meth)acrylate, polyurethane tri(meth)acrylate, polyurethane tetra(meth)acrylate, polyurethane penta(meth)acrylate and polyurethane poly(meth)acrylate.

When using a quite high energy light source, such as electron beams, α rays, β rays, γ rays or X rays, polymerization reaction can proceed without polymerization initiator. Since this is a conventionally known matter, the equipment is very expensive and the maintenance is complicated, this not described in detail in the present invention.

The photoradical polymerization initiators include, but are not limited to, a self-cleaving photopolymerization initiator and a hydrogen-abstracting polymerization initiator. These may be used alone, or in combination. Specific examples of the self-cleaving photopolymerization initiator include, but are not limited to, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methyl-1-propan-1-one, phenylglyoxylic acid methyl ester, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoylphosphine oxide, 1,2-octanedion-[4-(phenylthio)-2-(o-benzoyloxime)], ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), [4-(methylphenylthio)phenyl]phenylmethanone, and oligo {2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone}.

Specific examples of the hydrogen-abstracting polymerization initiator include, but are not limited to, benzophenone compounds such as benzophenone, methylbenzophenone, methyl-2-benzoylbenzoate, 4-benzoyl-4′-methyldiphenyl sulfide and phenylbenzophenone; and thioxanthone compounds such as 2,4-diethylthioxanthone, 2-chlorothioxanthone, isopropylthioxanthone and 1-chloro-4-propylthioxanthone.

Amines can be used together as a polymerization accelerator.

Specific examples thereof include, but are not limited to, p-dimethylaminobenzoate, 2-ethylhexyl p-dimethylaminobenzoate, methyl p-dimethylaminobenzoate, 2-dimethylaminoethyl benzoate and butoxyethyl p-dimethylaminobenzoate.

The photopolymerizable composition may be transparent without including a colorant, and may include a colorant when necessary. When the photopolymerizable composition is desired to be colorless or white, materials having less color are preferably used besides the polymerization initiator, the polymerization accelerator and the colorant.

Known inorganic pigments and organic pigments can be used as a colorant coloring the photopolymerizable composition.

Specific examples of black pigments include, but are not limited to, carbon black produced by a furnace method of a channel method.

Specific examples of yellow pigments include, but are not limited to, pigments of Pigment Yellow series, such as Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 75, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 95, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 114, Pigment Yellow 120, Pigment Yellow 128, Pigment Yellow 129, Pigment Yellow 138, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 154, Pigment Yellow 155, and Pigment Yellow 180.

Specific examples of magenta pigments include, but are not limited to, pigments of Pigment Red series, such as Pigment Red 5, Pigment Red 7, Pigment Red 12, Pigment Red 48(Ca), Pigment Red 48(Mn), Pigment Red 57(Ca), Pigment Red 57:1, Pigment Red 112, Pigment Red 122, Pigment Red 123, Pigment Red 168, Pigment Red 184, Pigment Red 202, and Pigment Violet 19.

Specific examples of cyan pigments include, but are not limited to, pigments of Pigment Blue series, such as Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 15, Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 16, Pigment Blue 22, Pigment Blue 60, Vat Blue 4, and Vat Blue 60.

Specific examples of white pigments include, but are not limited to, sulfuric acid salts of alkaline earth metals such as barium sulfate; carbonic acid salts of alkaline earth metals such as calcium carbonate; silica such as fine silicic acid powder and synthetic silicic acid salts; calcium silicate; alumina; alumina hydrate; titanium oxide; zinc oxide; talc; and clay.

In addition, various inorganic or organic pigments may be optionally used considering, for example, physical properties of the photopolymerizable composition.

Further, in the photopolymerizable composition, a polymerization inhibitor (e.g., 4-methoxy-1-naphthol, methylhydroquinone, hydroquinone, t-butylhydroquinone, di-t-butylhydroquinone, methoquinone, 2,2′-dihydroxy-3,3′-di(α-methylcyclohexyl)-5,5′-dimethyldiphenylmethane, p-benzoquinone, di-t-butyl diphenylamine, and 9,10-di-n-butoxyanthracene, 4,4′-[1,10-dioxo-1,10-decandiylbis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperidinyloxy), a surfactant (e.g., higher fatty acid ester containing polyether, an amino group, a carboxyl group, or a hydroxyl group, a polydimethylsiloxane compound containing, in its side chain or terminal, polyether, an amino group, a carboxyl group, or a hydroxyl group, and a fluoroalkyl compound containing a polyether residue, an amino group, a carboxyl group, and a hydroxyl group), and a polar group-containing polymer pigment dispersing agent may be optionally used.

The ink of the present invention can be housed in a container, and used as an ink cartridge. With this form, users do not have to directly touch the ink during operations, such as exchange of the ink, and thus there is no concern about staining of their fingers, hands, clothes, etc. In addition, it is possible to prevent interfusion of foreign matter such as dust into the ink.

The container is not particularly limited, and a shape, structure, size, and material thereof can be appropriately selected depending on the intended purpose. As for the container, for example, preferred is a container having an ink bag formed of an aluminum laminate film, or a resin film.

The ink cartridge will be explained with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram illustrating one example of an ink bag 241 of the ink cartridge, and FIG. 2 is a schematic diagram illustrating the ink cartridge 200, in which the ink bag 241 of FIG. 1 is housed in a cartridge case 244.

As illustrated in FIG. 1, the ink bag 241 is filled with the ink by injecting the ink from an ink inlet 242. After removal of air present inside the ink bag 241, the ink inlet 242 is sealed by fusion bonding. At the time of use, a needle attached to the main body of the device is inserted into an ink outlet 243 formed of a rubber member to supply the ink to the device therethrough. The ink bag 241 is formed of a wrapping member such as an air non-permeable aluminum laminate film. As illustrated in FIG. 2, the ink bag 241 is typically housed in a plastic cartridge case 244, which is then detachably mounted in various inkjet recording devices to thereby use as the ink cartridge 200.

The ink cartridge of the present invention is preferably detachably mounted in inkjet recording devices. The ink cartridge can simplify the refill and exchange of the ink to improve workability.

As for a coating base for the ink of the present invention, paper, plastic, metal, ceramic, glass, or a composite material thereof is used. Since a permeable base, such as wood free paper, can expect an effect of penetrating and drying, it is practical to use an aqueous ink or an oil ink, which is not a quick-drying ink, for such base. On the other hand, it is practical to use a quick-drying ink for a hard-permeation or a non-permeable base, such as gloss coat paper, a plastic film, a plastic molded article, ceramic, glass, metal, and rubber.

The ink of the present invention is preferably used on, but is not limited to, the surface of metals because of having good adherence thereto. In addition, the ink is preferably used on the non-permeable base as well because of being immediately cured upon application of light. Among the non-permeable bases, the ink of the present invention is suitably used for a plastic material, such as a plastic film, and a plastic molded article, which is formed of polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, an ABS resin, polyvinyl chloride, polystyrene, any of other polyesters, polyamide, a vinyl-based material, or a composite material thereof.

Examples

Having generally described this invention, further understanding can be obtained by reference to certain specific examples which are provided herein for the purpose of illustration only and are not intended to be limiting. In the descriptions in the following examples, the numbers represent weight ratios in parts, unless otherwise specified.

<Evaluation Method of SI Value>

According to the skin sensitization test based on the LLNA (Local Lymph Node Assay), the SI value was measured in the manner described below.

[Test Material] <<Positive Control>>

α-hexylcinnamaldehyde (HCA; product of Wako Pure Chemical Industries, Ltd.) was used as the positive control.

<<Medium>>

As a medium, a mixture containing acetone (product of Wako Pure Chemical Industries, Ltd.) and olive oil (product of Fudimi Pharmaceutical Co., Ltd.) in a volume ratio of 4/1 was used.

<<Animals Used>>

Before treated with the test substances, the positive control or the medium control, female mice were acclimated for 8 days including 6-day quarantine. No abnormalities were found in all the mice (used animals) during the quarantine/acclimation period.

Based on the body weights measured 2 days before the initiation of sensitization, they were categorized into 2 groups (4 mice/group) by the body weight stratified random sampling method so that the body weight of each individual was within ±20% of the average body weight of all the individuals. Each of the used animals was 8 weeks old to 9 weeks old at the time of the initiation of sensitization. The individuals remaining after the categorization were excluded from the test.

The used animals were individually identified by application of oil ink to their tale throughout the test period, and also their cages were labeled for identification.

<<Housing Environment>>

Throughout the housing period including the quarantine/acclimation period, the used animals were housed in an animal room with barrier system, which was set as follows: 21° C. to 25° C. in temperature, 40% to 70% in relative humidity, 10 times/hour to 15 times/hour in frequency of air circulation, and a 12 hour-interval lighting cycle (lighting from 7:00 to 19:00).

The housing cages used were those made of polycarbonate, and four animals were housed in each cage.

The used animals were given ad libitum solid feed for laboratory animals MF (product of Oriental Yeast Co., Ltd.). Also, using a water-supply bottle, the used animals were given ad libitum tap water in which sodium hypochlorite (PURELOX, product of OYALOX Co., Ltd.) had been added so that the chlorine concentration was about 5 ppm. Bedding used was SUNFLAKE (fir tree, shavings obtained with a power planer) (product of Charles River Inc.). The feed and all of the feeding equipments were sterilized with an autoclave (121° C., 30 min) before use.

The housing cage and the bedding were replaced with new ones at the times of the categorization and the removal of the auricular lymph node (i.e., the time when the animals were transferred from the animal room), and the water-supply bottle and rack were replaced with new ones at the time of the categorization.

[Test Method] <<Group Composition>>

The group compositions of the medium control group and positive control group used for the measurement of the Si value are shown in Table 1.

TABLE 1 Sensitization Number of Sensitization dose Times of animals Test group substance (μL/auricle) sensitization (animal No.) Medium Medium 25 Once/day × 4 control group only 3 days (1-4) Positive 25.0% HCA 25 Once/day × 4 control group 3 days (5-8)

[Preparation] <<Test Substance>>

Table 2 shows the amount of the test substance. The test substance was weighed in a measuring flask, and the volume of the test substance was adjusted to 1 mL with the medium. The thus-prepared test substance preparation was placed in a light-shielded airtight container (made of glass).

TABLE 2 Concentration after adjustment Mass of test (w/v %) substance (g) Test 50.0 0.5 substance

<<Positive Control Substance>>

About 0.25 g of HCA was accurately weighed, and the medium was added to the HCA to have the volume of 1 mL, to thereby prepare a 25.0% by mass solution. The thus-prepared positive control substance preparation was placed in a light-shielded airtight container (made of glass).

<<BrdU>>

In a measuring flask, 200 mg of 5-bromo-2′-deoxyuridine (BrdU, product of NACALAI TESQUE, INC.) was accurately weighed in a measuring flask. Then, physiological saline (product of OTSUKA PHARMACEUTICAL CO., LTD.) was added to the measuring flask, and dissolved through application of ultrasonic waves. Thereafter, the volume of the resultant solution was adjusted to 20 mL to prepare a 10 mg/mL solution (BrdU preparation). The BrdU preparation was sterilized through filtration with a sterilized filtration filter and placed in a sterilized container.

<<Preparation Day and Storage Period>>

The positive control preparation was prepared on the day before the initiation of sensitization, and stored in a cold place except in use. The medium and the test substance preparations were prepared on the day of sensitization. The BrdU preparation was prepared 2 days before administration and stored in a cold place until the day of administration.

[Sensitization and Administration of BrdU] <<Sensitization>>

Each (25 μL) of the test substance preparations, the positive control preparation or the medium was applied to both the auricles of each of the used animals using a micropipetter. This treatment was performed once a day for three consecutive days.

<<Administration of BrdU>>

About 48 hours after the final sensitization, the BrdU preparation (0.5 mL) was intraperitoneally administered once to each of the used animals.

[Observation and Examination] <<General Conditions>>

All the used animals used for the test were observed once or more times a day from the day of the initiation of sensitization to the day of the removal of the auricular lymph node (i.e., the day when the animals were transferred from the animal room). Notably, the observation day was counted from the day of the initiation of sensitization being regarded as Day 1.

<<Measurement of Body Weights>>

The body weight of each of the used animals was measured on the day of the initiation of sensitization and on the day of the removal of the auricular lymph node (i.e., the day when the animals were transferred from the animal room). Also, the average of the body weights and the standard error thereof were calculated for each group.

<<Removal of Auricular Lymph Node and Measurement of Weight Thereof>>

About 24 hours after the administration of BrdU, the used animals were allowed to undergo euthanasia, and their auricular lymph nodes were sampled. The surrounding tissue of each auricular lymph node was removed, and the auricular lymph nodes from both the auricles were collectively weighed. Also, the average of the weights of the auricular lymph nodes and the standard error thereof were calculated for each group. After the measurement of the weights, the auricular lymph nodes of each individual were stored in a frozen state using a BIO MEDICAL FREEZER set to −20° C.

<<Measurement of BrdU Intake>>

After returning the auricular lymph nodes to room temperature, the auricular lymph nodes were mashed with the gradual addition of physiological saline, and suspended therein. The thus-obtained suspension was filtrated and then dispensed into the wells of a 96-well microplate, with 3 wells being used per individual. The thus-dispensed suspensions were measured for intake of BrdU by the ELISA method. The reagents used were those of a commercially available kit (Cell Proliferation ELISA, BrdU colorimetric, Cat. No. 1647229, product of Roche Diagnostics Inc.). A multiplate reader (FLUOSTAR OPTIMA, product of BMG LABTECH Inc.) was used to measure the absorbance of each well (OD: 370 nm to 492 nm, the intake of BrdU), and the average of the absorbance of the 3 wells for each individual was used as the measurement of BrdU for the individual.

[Evaluation of Results] <<Calculation of Stimulation Index (SI)>>

As shown in the following formula, the measurement of BrdU intake for each individual was divided by the average of the measurements of BrdU intake in the vehicle control group to calculate the SI value for the individual. The SI value of each test group was the average of the SI values of the individuals. Also, the standard error of the SI values was calculated for each test group. Notably, the SI value was rounded at the second decimal place and shown to the first decimal place.

${SI} = \frac{\begin{matrix} {{{Averageof}\mspace{14mu} {measurements}\mspace{14mu} {of}\mspace{14mu} {BrdU}\mspace{14mu} {intake}}\mspace{14mu}} \\ {{for}\mspace{14mu} {each}\mspace{14mu} {individual}\; \left( {{average}\mspace{14mu} {of}\mspace{14mu} 3\mspace{14mu} {wells}} \right)} \end{matrix}}{\begin{matrix} {{{Averageof}\mspace{14mu} {measurements}\mspace{14mu} {of}\mspace{14mu} {BrdU}\mspace{14mu} {intake}\mspace{14mu} {in}\mspace{14mu} {the}}\mspace{14mu}} \\ {{vehicle}\mspace{14mu} {control}\mspace{14mu} {group}\; \left( {{average}\mspace{14mu} {of}\mspace{14mu} 4\mspace{14mu} {animals}} \right)} \end{matrix}}$

Examples 1 to 12 and Comparative Examples 1 to 3

The following materials (a), (b) and (c) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare inks of Examples and Comparative Examples.

(a) (Meth)acrylic acid ester having negative skin sensitization

(b) Methacrylic acid ester having a phosphoric group

(c) Photopolymerization initiator

TABLE 3-1 Com. Material Ex. 1 Ex. 1 Ex. 2 Ex. 3 a a1 95 80 80 80 a2 5 5 5 5 a3 b b1 15 b2 15 b3 15 c c1 20 20 20 20 Viscosity (mPa · s) 25° C. 7 16 19 15 45° C. *1 8 9 8 60° C. *1 *1 *1 *1 Ejection Head Temperature 25° C. 45° C. 45° C. 45° C. in Inkjet Printing Adherence Inkjet Aluminum 5 0 0 1 Printing Stainless 5 0 0 0 Brush Aluminum 5 0 0 0 coating Stainless 5 0 0 1

TABLE 3-2 Com. Material Ex. 2 Ex. 4 Ex. 5 Ex. 6 a a1 50 45 45 45 a2 a3 50 45 45 45 b b1 10 b2 10 b3 10 c c1 20 20 20 20 Viscosity (mPa · s) 25° C. 16 24 30 22 45° C. 8 10 13 9 60° C. *1 *1 *1 *1 Ejection Head Temperature 45° C. 45° C. 45° C. 45° C. in Inkjet Printing Adherence Inkjet Aluminum 5 0 0 0 Printing Stainless 5 0 0 1 Brush Aluminum 5 0 0 0 coating Stainless 5 0 0 0

TABLE 3-3 Com. Material Ex. 3 Ex. 7 Ex. 8 Ex. 9 a a1 70 60 60 60 a2 10 10 10 10 a3 20 20 20 20 b b1 10 b2 10 b3 10 c c1 15 15 15 15 Viscosity (mPa · s) 25° C. 14 27 31 26 45° C. 8 11 13 10 60° C. *1 *1 *1 *1 Ejection Head Temperature 45° C. 45° C. 45° C. 45° C. in Inkjet Printing Adherence Inkjet Aluminum 5 0 0 0 Printing Stainless 5 0 0 0 Brush Aluminum 5 0 0 1 coating Stainless 5 0 0 0

TABLE 3-4 Material Ex. 10 Ex. 11 Ex. 12 a a1 70 70 70 a2 a3 b b1 30 b2 30 b3 30 c c1 20 20 20 Viscosity (mPa · s) 25° C. 32 36 31 45° C. 15 18 14 60° C. *1 8 *1 Ejection Head Temperature in Inkjet Printing 45° C. 60° C. 45° C. Adherence Inkjet Aluminum 0 0 0 Printing Stainless 0 0 1 Brush Aluminum 0 0 1 coating Stainless 0 0 0 *1: Viscosity was not measured because the ink was ejectable at lower temperature.

Details of a1 to a8 and b1 are as follows. Values in ( ) at the ends are SI values in (1) LLNA test, and “None” means “negative for skin sensitization” or “no skin sensitization” in (2) MSDS (Material Safety Data Sheet).

(a) (Meth)acrylic acid ester having negative skin sensitization (a1 to a3) a1: diethyleneglycol dimethacrylate (n=2) “2G” from Shin-Nakamura Chemical Co., Ltd., (1.1) a2: caprolactone-modified dipentaerythritol hexaacrylate DPCA 60 from Nippon Kayaku Co., Ltd. (Negative in MSDS) a3: ethyleneoxide-modified trimethylolpropanetrimethacrylate (n=3) “TMPT-3EO” from Shin-Nakamura Chemical Co., Ltd., (1.0) (b) Methacrylic acid ester having a phosphoric group (b1 to b3) b1: Methacrylic acid ester including a phosphoric group having a formula (CH₂═C(CH₃)COOCH₂CH₂O)₂—P(═O)OH “LIGHT ESTER P-2M” from Kyoeisha Chemical Co. LTD. b2: Methacrylic acid ester including a phosphoric group having a formula (CH₂═C(CH₃)COOCH₂CH₂O—P(═O)(—OH)₂ “LIGHT ESTER P-1M” from Kyoeisha Chemical Co. LTD. b3: Methacrylic acid ester including a phosphoric group having a formula (CH₂═C(CH₃)COOCH₂CH₂OCO(CH₂)₅O)₂—P(═O)OII “KAYAMER PM21” from NIPPON KAYAKU Co., Ltd. (c) Photopolymerization initiator (c1) c1: 1-hydroxycyclohexylphenylketone “Irgacure 184” from BASF (Negative in MSDS)

The viscosity (mPa·s) and the strength of coating film at 25, 45 and 60° C. of each ink were measured.

The viscosity of each ink was measured by a cone plate-type rotary viscometer (manufactured by TOKI SANGYO CO., LTD.) with the temperature of circulating water being constantly set 25, 45 and 60° C. The temperature of 25° C. is temperature set considering typical room temperature. The temperatures of 45 and 60° C. are temperatures of a heatable marketed inkjet ejection head such as GEN4 from Ricoh Printing Systems, Ltd.

The photopolymerizable composition prepared at a predetermined combination was used as it was in evaluation by brush coating. To evaluate inkjet ink, after the ink was filtered through a membrane filter made of fluorine resin, having a pore diameter of 5 microns, the ink was sealed in an aluminum pouch bag having the shape in FIG. 1 so that a bubble was formed. The pouch bag the ink was sealed in was contained in a plastic cartridge as shown in FIG. 2. In a chassis capable of containing the cartridge, an ink flow channel was formed from the cartridge to the GEN4 head from Ricoh Printing Systems, Ltd. to eject the ink and form a solid coating film. Each of the brush coating and the inkjet printing was controlled to form a solid coating film having a thickness about 40 microns.

A solid coating film formed on a marketed aluminum-laminated polyethyleneterephthalate film (ALPET 9-100 having a thickness of 100 microns from PANAC Corp.) and a solid coating film formed on a general use stainless plate (SUS304 having a thickness of 0.5 mm) were irradiated at 0.3 W/cm² and 1.2 J/cm² and hardened so as to evaluate adherence and strength thereof.

Scratch hardness of the irradiated and hardened coating film was evaluated by a pencil method specified in JIS-K-5600-5-4. Pencil hardness includes 2H, H, F, HB, B, 2B to 6B in descending order of hardness.

The adherence of the solid coating film hardened by irradiation was evaluated by a crosscut method specified in JIS-K-5600-5-6. Tape peeling test was performed on tessellated 25 squares formed at an interval of 1 mm to visually observe the remaining squares and classify them into 6 ranks (0 to 5). Zero (0) means no peeling of the square and good adherence. The larger, the worse. The details are omitted because of being disclosed in JIS-K-5600-5-6.

The evaluation results are shown in Tables 3-1 to 3-4 and 4-1 to 4-3.

TABLE 4-1 Material Ex. 1 Ex. 2 Ex. 3 Ex. 4 a a1 80 80 80 45 a2 5 5 5 a3 45 b b1 15 10 b2 15 b3 15 c c1 20 20 20 20 Coating Inkjet B 2B 3B HB Film Printing Strength Brush B 2B 3B HB Coating

TABLE 4-2 Material Ex. 5 Ex. 6 Ex. 7 Ex. 8 a a1 45 45 60 60 a2 10 10 a3 45 45 20 20 b b1 10 b2 10 10 b3 10 c c1 20 20 15 15 Coating Inkjet B 2B F HB Film Printing Strength Brush B 2B F HB Coating

TABLE 4-3 Material Ex. 9 Ex. 10 Ex. 11 Ex. 12 a a1 60 70 70 70 a2 10 a3 20 b b1 30 b2 30 b3 10 30 c c1 15 20 20 20 Coating Inkjet 2B 2B 6B 6B Film Printing Strength Brush 2B 2B 6B 6B Coating

As Tables 3-1 to 3-4 show, (b) methacrylic acid ester having a phosphoric group improves adherence to metal surfaces. Particularly, the methacrylic acid esters having a phosphoric group b1 having the formula (CH₂═C(CH₃)COOCH₂CH₂O)₂—P(═O)OH or b2 having the formula CH₂═C(CH₃)COOCH₂CH₂O—P(═O)(—OH)₂ more improve the adherence.

Further, methacrylic acid ester having a phosphoric group b1 having the formula (CH₂═C(CH₃)COOCH₂CH₂O)₂—P(═O)OH particularly improves strength of the coating film.

There were no noticeable differences between coating films formed by the inkjet printing and the brush coating. All the photopolymerizable compositions and the inks had no particular odors to be cautioned.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth therein. 

What is claimed is:
 1. A photopolymerizable composition, comprising: diethyleneglycol dimethacrylate; and methacrylic acid ester having a phosphoric group.
 2. The photopolymerizable composition of claim 1, wherein the methacrylic acid ester having a phosphoric group comprises a structure having the following formula: (CH₂═C(CH₃)COOCH₂CH₂O)₂—P(═O)OH
 3. The photopolymerizable composition of claim 1, further comprising caprolactone-modified dipentaerythritol hexaacrylate.
 4. The photopolymerizable composition of claim 1, further comprising ethyleneoxide-modified trimethylolpropane trimethacrylate.
 5. An inkjet ink, comprising the photopolymerizable composition according to claim
 1. 6. A cartridge containing the inkjet ink according to claim
 5. 7. A coated matter coated with the photopolymerizable composition according to claim
 1. 